Answer
$y-13=-9(x-8)$
Work Step by Step
This form is known as point-slope form which means we substitute our coordinates and the given slope, $m$ into the formula,
$y-y_1=m(x-x_1)$ where $(x_1,y_1)$ is the point.
$(8,13)$ is the point, $m=-9$
$y-13=-9(x-8)$
